Role of gas-particle conversion of ammonia in haze pollution under ammonia-rich environment in Northern China and prospects of effective emission reduction.

As an important precursor of secondary inorganic aerosols (SIAs), ammonia (NH3) plays a key role in fine particulate matter (PM2.5) formation. In order to investigate its impacts on haze formation in the North China Plain (NCP) during winter, NH3 concentrations were observed at a high-temporal resolution of 1 min by using the SP-DOAS in Tai'an from December 2021 to February 2022. During the observation period, the average NH3 concentration was 11.84 ± 5.9 ppbv, and it was determined as an ammonia-rich environment during different air quality conditions. Furthermore, the average concentrations of sulfate (SO42-), nitrate (NO3-) and ammonium (NH4+) were 9.54 ± 5.97 µg/m3, 19.09 ± 14.18 µg/m3 and 10.72 ± 6.53 µg/m3, respectively. Under the nitrate-dominated atmospheric environment, aerosol liquid water content (ALWC) was crucial for NH3 particle transformation during haze aggravation, and the gas-particle partitioning of ammonia played an important role in the SIAs formation. The reconstruction of the molecular composition further indicated that ammonium nitrate (NH4NO3) plays a dominant role in the increase of PM2.5 during haze events. Consequently, future efforts to mitigate fine particulate pollution in this region should focus on controlling NH4NO3 levels. In ammonia-rich environments, NO3- formation is more dependent on the concentration of nitric acid (HNO3). The sensitive analysis of TNO3 (HNO3 + NO3-) and NHX (NH3 + NH4+) reduction using the thermodynamic model suggested that the NO3- concentration decreases linearly with the reduction of TNO3. And the concentration of NO3- decreases rapidly only when NHX is reduced by 50-60 %. Reducing NOX emissions is the most effective way to alleviate nitrate pollution in this region.

Comparison of antibiotic resistance and copper tolerance of Enterococcus spp. and Lactobacillus spp. isolated from piglets before and after weaning.

In China, antimicrobials and copper are used extensively as growth-promoting agents for piglets. This study aimed to characterize the role of in-feed copper in the emergence of copper-tolerant and antibiotic-resistant Enterococcus and Lactobacillus isolates in Chinese pig farms. Feces of the same eight piglets from four litters at 7 and 55 days old and their mothers were traced in order to isolate Enterococcus spp. and Lactobacillus spp.. The minimum inhibitory concentrations of 10 antimicrobials and copper sulfate were determined using an agar dilution method. The feed levels of Cu2+ for lactating sows, suckling piglets, and weaned piglets were 6, 177, and 18 mg/kg, respectively. All the 136 Enterococcus isolates were sensitive to vancomycin; and the resistance rates to penicillin, enrofloxacin, and high level streptomycin resistance increased significantly after weaning. For the 155 Lactobacillus isolates, the resistance rates to ampicillin, chloramphenicol, tetracycline, and enrofloxacin were significantly higher in weaned piglets. The ratios of copper tolerant Enterococcus and Lactobacillus isolates both increased significantly after weaning (P < 0.05). A phenotypic correlation was observed after classifying the isolates into two groups (CuSO4 MIC50 < 16 or ≧16 for enterococci; CuSO4 MIC50 < 12 or ≧12 for lactobacilli) and comparing the antimicrobial-resistant percentage of two groups. On species level, a significant increase of E. faecalis to enrofloxacin was observed in line with the increase of copper MIC (P < 0.05). The findings revealed the changes of the antibiotic resistance and copper tolerance level of enterococci and lactobacilli between suckling and weaned piglets and demonstrated that there might be a strong association between in-feed copper and increased antibiotic resistance in enterococci and lactobacilli in Chinese intensive swine farms.

[Accumulation of antibiotics, heavy metals and antimicrobial-resistant bacteria in duck bio-bed].

OBJECTIVE: The objective of this study is to understand the accumulation of antibiotics, metals in the litter, and evolution features of bacterial antimicrobial-resistance during the fermentation of duck bio-bed. METHODS: The experiment was conducted in meat duck bio-bed farm of Jiangsu province from November 2011 to July 2013. The new litter and spent litter from 4th, 8th meat duck flock were studied for the accumulation of consumed antimicrobials and metals. Bacterial resistance levels to consumed antimicrobials were measured in the collected litter. RESULTS: The residues of doxycycline in the litter increased significantly after successive flocks of meat ducks, but ofloxacin had not been detected in all litter samples. The litter for the 8th meat duck flock had the highest level of resistant cultivable bacteria in the three sorts of medium amended with 16 microg/mL, 100 microg/mL doxycycline. Meanwhile, the level of resistant cultivable bacteria in the same sort of medium amended with 8 microg/mL, 50 microg/mL ofloxacin differed insignificantly between different flock litter sample. Different flock litter differed insignificantly in the accumulation content of As, Pb and Hg, and was low in Cd. The 4th, 8th flock litter increased significantly in Zn and Mn than new litter, and increased slowly in Cu and Cr. CONCLUSION: With the application of doxycycline in each flock of meat ducks, the content of doxycycline and doxycycline resistance in enterobacteriaceae bacteria in the litter increased significantly, Zn and Mn had an increasing trend overall.